May 5, 2021Summer Sanitation Is Important as Ever
To contact John Palumbo go to: jpalumbo@ag.Arizona.edu
Contact herbicides are those that only affect the part of the weed that they “contact” They don’t move into or affect any other part of a plant. They were the first herbicides used and surprisingly, they still are better at controlling some weeds than any other products that have been developed. They usually control only small weeds with good coverage although some of them will kill large malva , Purslane and some other difficult to kill weeds. Goal, Sharpen, Treevix and Gramoxone, which are all contacts, will kill malva and purslane while systemic herbicides like Glyphosate and 2,4-D, misses them. Maestro or Bucril (Bromoxynil), also an old contact, will kill swinecress while many systemics like the growth regulators ,miss it. Glufosinate( Liberty, Rely) is a contact that is very broad spectrum and kills more grasses and broadleaves than many systemic herbicides. These all work very fast and in this age of immediate gratification ,you don’t have to wait long. Most have little soil residual activity (except Goal, Chateau and a couple others) Goal and Chateau are contacts but used mostly preemergence to the weeds. They “ contact” the weeds when they emerge at the surface. which is a benefit where double or triple cropping is common. Most( again except Goal) are not volatile but will cause pretty clear contact injury when the spray moves to sensitive crops. Paraquat was registered in 1959 and is still a very useful tool for desiccating plants. Many restrictions have been put on its use because of its toxicity to humans. Most contact herbicides are non-selective and will injure most living plant tissue. They are used selectively with directed spray or timing. Adjuvants are often required to increase absorption, spreading and sticking.
In the past couple of weeks, the reports of INSV in fields has increased dramatically. INSV has been found in fields in Yuma/Gila Valley, Wellton, Tacna, Roll, and Imperial Valley.
PCAs have reported thrips pressure as low this year and most fields have infection less than 1% but some fields have been reported to have higher incidence. The virus has been detected in direct seeded field as well as transplants imported from Salinas, CA.
Impatiens necrotic spot virus, also known as INSV is a tospovirus closely related to Tomato spotted wilt virus. Infected plants usually have leaves with brown to dark brown necrotic areas. Sometimes the symptoms may be confused with “chemical burn”. As necrosis progresses the leaf browns or die out. Plants infected in early stage may become stunted and die, or become unmarketable.
What makes this virus of high economic importance?
The plants become unmarketable which is the ultimate economic loss. But there are factors that facilitate the virus outbreak.
The first one is efficient transmission by its vector (s). The virus is transmitted by western flower thrips, Frankliniella occidentalis.
If you remember our virus transmission series in past newsletters, thrips transmit viruses in persistent propagative manner. Insects have to feed on virus infected plants for hours/days to acquire the virus and the virus has to incubate for hours/days in the insect. After insect can transmit the virus throughout its lifespan. The virus can multiply in the vector system and often times the virus particles are also passed on to the insect offspring. Adult thrips can transmit these viruses only if acquired in the larval stage of development. Larval thrips will feed on a virus-infected plant, pupate, and emerge as a winged adult capable of transmitting the virus. The thrips then will carry the virus for life.
The next contributing factor is host range. INSV infects large number of ornamental and vegetable plants. We are talking 600 species of plants that are susceptible to INSV and thrips love flowers.
While it may not be practical to remove all your ornamentals in fear of INSV, it is definitely practical to monitor thrips population in your field. As the legend says “When in doubt, scout”.
And if you need diagnosis, drop the samples in the clinic! But then if you have immunostrips, you don’t have to make the drive to the Ag Center!
DIY testing: Impatiens necrotic spot virus (INSV)
As visual diagnosis of the virus is confusing and could even be misleading at times, it is very important to confirm a symptomatology via clinical diagnosis.
The good news is there are tools available for quick and easy diagnosis of INSV. You can order the immunostrips from Agdia (https://orders.agdia.com/agdia-immunostrip-for-insv-isk-20501)
The immunostrips cost anywhere from $5-20 depending on how much you buy. They perform better when they stay refrigerated until just before use.
Immunostrips are quick and easy tool to use. The kit comes with a buffer bag and immunostrip.
One band means that the positive control worked which means the system worked. Sometimes you see no bands at all. This means the system did not work and you have to repeat the test.
If you are seeing symptoms in your field please let Bindu Poudel-Ward know via email (firstname.lastname@example.org or text (928-920-1110). Please keep a note of weed species you are consistently seeing in your fields and keep the thrips population under check.
There are many innovative automated weeding technologies coming out of Europe. One of these is the autonomous weeding robot being developed by Ecoroboti (Yverdon-les-Bains, Switzerland). The device is lightweight and solar powered. Early prototypes used a spider like, three-axis delta robot to precisely deliver herbicides to target weeds. Videos of the device were futuristic and intriguing to watch. The company has since moved on to a simpler weeding robot equipped with a fixed boom for spot spraying weeds (Fig. 1 & 2). The autonomous robot has some specifications that are plausible for use in Arizona vegetable production. Machine travel speed is 2.2 mph and work rate is 15 acres/day (10 hour day). Spot spray resolution is reasonable at 2.5 inch2 (1.5 x 1.5 inch). This is accomplished using a series of 52 nozzles mounted on an 80 inch wide boom (Fig. 2). The machine uses computer imaging and artificial intelligence for crop/weed differentiation to identify and target weeds.
This past summer, the system was tested in sugar beets in Germany. Results showed the system correctly sprayed about 80% of the weeds. For a first time, real-world, field scale test, this outcome is encouraging.
There are some limitations however. According to product literature, the machine’s artificial intelligence system will identify a crop plant as a weed approximately 5% of the time. Given the high value of vegetable crops, killing 5% of the crop as a trade-off for robotically controlling weeds is probably not viable. It should be noted that this level of crop/weed recognition performance is consistent with other artificial intelligence-based systems reported in the literature.
Don’t give up hope though. This type of technology is advancing rapidly, and may become feasible in the future. Computing speed and sensor capabilities are advancing all the time. A review of literature indicates that systems that combine 3-D morphology, optical color and accurate location data with deep learning techniques may be a viable approach to reliably differentiate crops from weeds. It will be interesting and exciting to watch this technology as it develops. That’s for sure.
As I have mentioned before, automated thinning and weeding technologies are advancing at a very rapid pace. If you know of a new technology that would be of interest and appropriate for this newsletter, please feel free to contact me.
The Yuma County Leaf Wetness Network remains in place for the 2018/19 vegetable season. Growers and PCAs may access information generated by the network by entering the following internet address: http://18.104.22.168:460
Upon entering the address above, you will be transferred to internet page that provides a series of tabs at the top of the page. Simply click on the tabs to access the information of interest.
Results of pheromone and sticky trap catches can be viewed HERE.
Results of pheromone and sticky trap catches can be viewed HERE.
Corn earworm: CEW moth activity increased a bit in the past 2 weeks but remains well below average for late spring.
Beet armyworm: Moth counts increased slightly, but remain very low consistent with seasonal temperatures, and below average for this point in the season.
Cabbage looper: Significant increase in activity in Dome Valley, Gila Valley and Tacna, but moth counts remain unusually low for this time of year, as they have all season.
Whitefly: No adult movement recorded across all locations and overall low numbers consistent with temperatures.
Thrips: Thrips adult movement beginning to pick up considerably, particularly in Yuma and Dome Valleys. Movement is below average for late March.
Aphids: Seasonal aphid counts down considerably compared with the Feb and Jan. Counts highest in Bard and Gila Valley. Below average movement for this time of year. Majority of species found on traps were green peach aphid.
Leafminers: Adult activity up slightly in some locations, but well below average for late season.